The present invention relates to the manufacture of integrated circuits. Specifically, a method and apparatus are described for accurately determining the end point of a polishing operation.
In the manufacture of integrated circuit substrates, chemical-mechanical polishing processes are carried out on the substrate to planarize various layers which have been deposited on the substrate. The process of polishing the surface of a semiconductor requires that an accurate determination be made as to when polishing is to cease. Various techniques have been developed to detect the required polishing end point, including the measurement of the friction between a substrate and a polishing pad, sensed by monitoring the changing motor torque requirements, as well as measuring the temperature of the polishing pad surface, optical inspection of the wafer surface, measurement of surface conductivity, etc.
As the feature dimensions of an integrated circuit are reduced, it becomes more critical to be able to precisely determine end point, and to avoid either underpolishing or overpolishing the substrate. If substrates are underpolished, electrical defects such as conductor shorting and open contacts may result increasing the amount of rework necessary. Overpolishing of substrates impacts on electrical performance, and results in lower yields when layer thicknesses are reduced below specification.
The ability to precisely determine polishing end point, and controlling polishing in response to an accurately detected end point reduces the problems associated with the overpolishing and underpolishing of substrates.